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  <title>Document</title>
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<body>
  <script>
    let arr = [1, 2, 3, 4, 5]
    arr.forEach((i, index, arr) => {
      // console.log(`i`, i);
      // console.log(`index`, index);
      // console.log(`arr`, arr);
      arr.flag = false
      // console.log(arr);
      //修改原数组会改变
    })
    let res = arr.map((i) => {
      return i * 2
    })
    console.log(res);
    /*
      区别:
      map:分配内存空间存储新数组，并且返回
      foreach：不会返回，返回的话是undefined
    
    */
    // for (let i of arr) {
    //   console.log(i);
    // }
  </script>
</body>

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